1. From U.S. patent document No. 3503754, for example, a pig with an axial valve system is known, where the pig can be anchored in a pipeline by means of pins which are inserted through the pipeline walls from the outside and against which the pig is secured. The pig according to the patent document shall primarily be used for shut-off of the fluid flow during brief periods of pipeline repairs etc., and can not be permanently installed.
2. From U.S. patent document No. 3746026 a blocking pig is known which features parking brakes and sealing devices for temporary shutoff of a pipeline at a predetermined point. The blocking pig, however, lacks a separate valve function, and consequently cannot be permanently installed in a pipeline either.
From DE patent document No. 3142768, an internal blocking device for a pipeline is known which comprises two flanges and a cylinder connecting these. Outside the cylinder, on the outermost part between said cylinder and the pipeline wall, an elastic tube has been installed, consisting of a rubber-type, synthetic material, which is reinforced with several layers of metal sheathing. Inside the tube, an inflatable bellow is mounted which receives pressure medium from pressure bottles located inside the cylinder. The tube and the inflatable bellow have a double function in that both shall seal off fluid which flows into the pipeline and anchor the blocking device in the pipeline. The blocking device does not feature a separate valve function, and must therefore be inserted into the pipeline each time the pipeline is to be blocked.